1. Field of the Invention
The present invention relates to image processing apparatuses, image processing methods and programs to cause computers to perform image processing. More particularly, the present invention relates to an image processing apparatus, an image processing method and a program to cause a computer to perform image processing that allow high-precision color conversion of an image.
2. Description of the Related Art
Conventionally, a technique for reading an image from an original with a reading device like a scanner, performing color conversion with a computer connected to a network, and outputting the image to a printer or the like is known.
For example, Japanese Patent Laying-Open No. 11-177754 discloses a scanner system in which the system having a plurality of scanners connected to a network determines which scanner to use, in terms of hardware, according to an input condition of the original.
For color conversion of an image, a color information file (or a color conversion file, e.g., an ICC (International Color Consortium) profile) specific to a device is referred to, which is created based on representative colors. The file defines color information specific to the device, and is used for exchanging the color information with another device.
The color conversion file generally stores data of representative colors picked up considerably roughly from a color space that the relevant device is able to reproduce, and data of the corresponding colors in another color space, by correlating the data with each other. Color conversion of the colors having not been picked up are carried out by interpolation. This type of color conversion employing interpolation from roughly picked up colors, however, is disadvantageous because the precision in color conversion is degraded.
For example, if colors R, G and B are represented with 8 bits each, each color can be expressed with 256-step gradation. In the combination of RGB, approximately 16,770,000 colors can be expressed.
To handle these colors, measuring all the 16,770,000 colors and preparing color conversion files (look-up tables) by correlating them with, e.g., L*a*b* data would be unrealistic, since it requires an enormous file capacity. In practice, it is common to pick up each color of RGB every 10 steps of gradation or so to obtain data of less than 1,000 colors, and to prepare color conversion files correlating the obtained data with L*a*b* data. In this case, data of the colors having not been picked up are obtained by interpolation, which often results in insufficient precision for fine color reproduction.